1. Field of the Invention
The present invention relates to an information recording apparatus that causes information light and reference light to interfere with each other to thereby record an interference image on a recording surface of a recording medium and an information reproducing apparatus that reproduces information included in the interference image recorded on the recording medium.
2. Description of the Related Art
Various apparatuses that record information on a recording surface of a recording medium as an interference image and reproduce the information recorded as the interference image have been proposed. Some of the apparatuses are disclosed in, for example, Non-Patent Document 1. The Non-Patent Document 1 is the following document.
Non-Patent Document 1: Hideyoshi Horimai, et al., “Holographic Medium about to Take Off: 200 Gigabyte to be realized in 2006” Nikkei Electronics, Nikkei Business Publications, Inc., Jan. 17, 2005, No. 891, p. 105 to 114
FIG. 13 is a diagram for schematically explaining a structure of a main part of an information recording apparatus disclosed in the Non-Patent Document 1. In this apparatus, light emitted from a not-shown light source is split into two light beams by a beam splitter 101. One of the light beams is modulated according to a pattern displayed on an SLM (Spatial Light Modulator) 102 and emitted as information light. The information light is made incident on a recording medium 104 through an object lens 103. On the other hand, the other light beam split by the beam splitter 101 is made incident on the recording medium 104 as reference light through optical members such as lenses and a mirror. On the recording medium 104, the information light and the reference light interfere with each other and information corresponding to the display pattern is recorded as an interference image (an interference fringe).
When the reference light is irradiated on the recording medium 104 in a direction same as that during recording, light is reproduced from the recording medium 104. This light is focused on a light-receiving element 106 made of, for example, CMOS, through the object lens 105. This makes it possible to read out (reproduce) the information recorded on the recording medium 104 as a two-dimensional image.
FIGS. 14A and 14B are perspective views schematically showing a structure of a main part of another information recording apparatus disclosed in the Non-Patent Document 1. In this apparatus, during recording of information, as shown in FIG. 14A, a pattern for information light 201a is displayed in the center of an SLM 201 and, on the other hand, a pattern for reference light 201b is displayed on a periphery of the SLM 201. A laser beam is irradiated on the SLM 201 from a light source (not shown). Information light (light in the center of the laser beam) and reference light (light in a periphery of the laser beam) are emitted from the SLM 201. These lights are converged by an object lens 202 and condensed on a recording surface of the recording medium 203. In this case, the information light and the reference light interfere with each other, whereby information corresponding to the pattern 201a is recorded as an interference image on the recording surface.
On the other hand, during reproduction of information, as shown in FIG. 14B, only the pattern for reference light 201b same as that during recording is displayed on the SLM 201 and a laser beam from the light source is irradiated on the SLM 201. In this case, only the reference light is emitted from the SLM 201 and irradiated on the recording medium 203 through a beam splitter 204 and an object lens 202. Light having the information recorded as the interference image is reproduced from the recording medium 203. The reproduced light returns in the direction of the object lens 202, changes the direction in the beam splitter 204, and is received by a light-receiving element 205. In the light-receiving element 205, a reproduced image is detected as a two-dimensional image.
In recording information on a recording medium using the holographic technique described above, for example, as shown in FIG. 15, by shifting a recording medium 302 by a very small distance every time when an interference image 301 is recorded, it is possible to multiply record the interference image 301 to thereby increase a recording capacity of the recording medium 302. In such a shift multiple recording system, according to rotational or parallel shift of the recording medium 302, it is possible to record the interference image 301 such that spots S are arranged in a spiral shape as shown in FIG. 16 or record the interference image 301 such that the spots S are arranged in a concentric circle shape as shown in FIG. 17.
However, since the recording medium is generally large, in rotating the recording medium to multiply record an interference image, a state of the recording medium during the rotation (warp, eccentricity, swing, etc. of the recording medium) substantially affects the recording of the interference image. Therefor, in order to accurately record the interference image, it is necessary to perform rotation control always taking into account the state of the recording medium. As a result, the control and the structure of the apparatus are complicated.